delicious, yet low-key in cambridge?

I'm new to Boston and need help on where to bring visiting parents this weekend. We have a reservation at Oleana, but still looking for the other nights.

I spent a while looking at all your recommendations for Beacon Hill and Cambridge, and the most recommended places all seem to be in the range of $20+ entrees. Is there anything slightly less expensive that might fit the bill?

Central Square would be best, but happy to travel on the Red Line too. Many thanks!